[RFC PATCH v2 2/2] ARM: kernel: update cpuinfo to print all online CPUs features

[Lorenzo Pieralisi]

Currently, reading /proc/cpuinfo provides userspace with CPU ID of
the CPU carrying out the read from the file. This is fine as long as all
CPUs in the system are the same. With the advent of big.LITTLE and
heterogenous ARM systems this approach provides user space with incorrect
bits of information since CPU ids in the system might differ from the one
provided by the CPU reading the file.

This patch updates the cpuinfo show function so that a read from
/proc/cpuinfo prints HW information for all online CPUs at once, mirroring
 x86 behaviour.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
---
 arch/arm/kernel/setup.c | 66 ++++++++++++++++++++++++-------------------------
 1 file changed, 33 insertions(+), 33 deletions(-)

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 20c530b..948fff1 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -842,13 +842,15 @@ static const char *hwcap_str[] = {
 
 static int c_show(struct seq_file *m, void *v)
 {
-	int i;
+	int i, j;
+	u32 cpuid;
 
-	seq_printf(m, "Processor\t: %s rev %d (%s)\n",
-		   cpu_name, read_cpuid_id() & 15, elf_platform);
+	for_each_online_cpu(i) {
+		cpuid = is_smp() ? per_cpu(cpu_data, i).cpuid : read_cpuid_id();
+		seq_printf(m, "Processor\t: %s rev %d (%s)\n",
+			   cpu_name, cpuid & 15, elf_platform);
 
 #if defined(CONFIG_SMP)
-	for_each_online_cpu(i) {
 		/*
 		 * glibc reads /proc/cpuinfo to determine the number of
 		 * online processors, looking for lines beginning with
@@ -858,42 +860,40 @@ static int c_show(struct seq_file *m, void *v)
 		seq_printf(m, "BogoMIPS\t: %lu.%02lu\n\n",
 			   per_cpu(cpu_data, i).loops_per_jiffy / (500000UL/HZ),
 			   (per_cpu(cpu_data, i).loops_per_jiffy / (5000UL/HZ)) % 100);
-	}
-#else /* CONFIG_SMP */
-	seq_printf(m, "BogoMIPS\t: %lu.%02lu\n",
-		   loops_per_jiffy / (500000/HZ),
-		   (loops_per_jiffy / (5000/HZ)) % 100);
+#else
+		seq_printf(m, "BogoMIPS\t: %lu.%02lu\n",
+			   loops_per_jiffy / (500000/HZ),
+			   (loops_per_jiffy / (5000/HZ)) % 100);
 #endif
+		/* dump out the processor features */
+		seq_puts(m, "Features\t: ");
 
-	/* dump out the processor features */
-	seq_puts(m, "Features\t: ");
+		for (j = 0; hwcap_str[j]; j++)
+			if (elf_hwcap & (1 << j))
+				seq_printf(m, "%s ", hwcap_str[j]);
 
-	for (i = 0; hwcap_str[i]; i++)
-		if (elf_hwcap & (1 << i))
-			seq_printf(m, "%s ", hwcap_str[i]);
+		seq_printf(m, "\nCPU implementer\t: 0x%02x\n", cpuid >> 24);
+		seq_printf(m, "CPU architecture: %s\n",
+			   proc_arch[cpu_architecture()]);
 
-	seq_printf(m, "\nCPU implementer\t: 0x%02x\n", read_cpuid_id() >> 24);
-	seq_printf(m, "CPU architecture: %s\n", proc_arch[cpu_architecture()]);
-
-	if ((read_cpuid_id() & 0x0008f000) == 0x00000000) {
-		/* pre-ARM7 */
-		seq_printf(m, "CPU part\t: %07x\n", read_cpuid_id() >> 4);
-	} else {
-		if ((read_cpuid_id() & 0x0008f000) == 0x00007000) {
-			/* ARM7 */
-			seq_printf(m, "CPU variant\t: 0x%02x\n",
-				   (read_cpuid_id() >> 16) & 127);
+		if ((cpuid & 0x0008f000) == 0x00000000) {
+			/* pre-ARM7 */
+			seq_printf(m, "CPU part\t: %07x\n", cpuid >> 4);
 		} else {
-			/* post-ARM7 */
-			seq_printf(m, "CPU variant\t: 0x%x\n",
-				   (read_cpuid_id() >> 20) & 15);
+			if ((cpuid & 0x0008f000) == 0x00007000) {
+				/* ARM7 */
+				seq_printf(m, "CPU variant\t: 0x%02x\n",
+					   (cpuid >> 16) & 127);
+			} else {
+				/* post-ARM7 */
+				seq_printf(m, "CPU variant\t: 0x%x\n",
+					   (cpuid >> 20) & 15);
+			}
+			seq_printf(m, "CPU part\t: 0x%03x\n",
+				   (cpuid >> 4) & 0xfff);
 		}
-		seq_printf(m, "CPU part\t: 0x%03x\n",
-			   (read_cpuid_id() >> 4) & 0xfff);
+		seq_printf(m, "CPU revision\t: %d\n\n", cpuid & 15);
 	}
-	seq_printf(m, "CPU revision\t: %d\n", read_cpuid_id() & 15);
-
-	seq_puts(m, "\n");
 
 	seq_printf(m, "Hardware\t: %s\n", machine_name);
 	seq_printf(m, "Revision\t: %04x\n", system_rev);
-- 
1.7.12